Substrata having anisotropic thermal expansion properties are important for many electronic products incorporating microelectronic components or devices. Typically, microelectronic components including a substrate are contained in a package for ease of use and for protection from damage which might occur, for example, during shipping, testing and/or during installation. Often it is desirable to affix a microelectronic component to a package base by means of an adhesive, such as solder or some form of glue. Materials employed in the art include room temperature vulcanizing silicone rubbers, epoxies, thermoplastic materials and other organic, inorganic and quasiorganic substances. Package bases comprise materials having isotropic thermal expansion properties (e.g., metals, ceramics) or anisotropic thermal expansion properties (e.g., woven laminated materials).
Problems often encountered due to differences in thermal expansion coefficients between substrates and package bases include de-lamination of the substrate from the package base and fracture of the substrate and/or package base. A further problem is encountered in stress-induced distortion of device responses because of temperature changes and differences in temperature coefficients of expansion. These problems are exacerbated when the substrate has anisotropic thermal expansion properties and the package base has isotropic thermal expansion properties or anisotropic properties differing from those of the substrate.
One approach to avoiding fracture of the substrate and/or package base is to employ a relatively soft adhesive layer. This often renders the device susceptible to de-lamination and may also result in unacceptable stresses within the substrate when the packaged device is thermally cycled.
What are needed are methods and apparatus for substrate attachment which provide reduced thermal-induced stresses and robust bonding for substrates having anisotropic thermal expansion characteristics.